Sorry if I confused you.Are we to have axions or MiHsC?Both are speculative but only one or none can be true, I think.What do you chaps think?

1) Eubanks posted a paper about Dark Matter, stating <<While I guess it is possible, I just don't buy it>>.

2) We have been posting the predictive formulas of Dr. McCulloch, Shawyer and @NotSoSureOfIt not as partisans for one or another, but in order to find out the truth, whatever the truth ends up to be.

3) This technology is such a breakthrough that it holds my interest if it would be possible to use it for spaceflight. Count me as an initial skeptic that carefully would like to rule out all classical physics explanations first, one by one. If the explanation requires exotic physics, this will naturally manifest on its own, just like it happened with Quantum Mechanics at the early 20th century. There is no need for a scientist to be partisan to any given theory. Experiments will tell the truth.

I think that there is a truth out there in the Universe independent of mankind. Scientists are like explorers trying to find it. People with passionate beliefs are more unlikely to find it than those with an open mind.

More thoughts on Dark Matter & the EM Drive (thanks for fixing the dead link!)

Suppose DM is some particle (axions or whatever) with a mass of 2 GHz = 8 micro-eV = 1.48 x 10^-41 kg. The Halo dark matter flux is ~ 2 x 10^-17 kg / (m^2 s sr), so that's 1.4 x 10^24 particles / (m^2 s sr) each (on average) at 300 km/sec. So, the thrust flux from these, if you absorbed them perfectly, would be M * v * that number flux ~ 6 x 10^-12 Newtons / (m^2 sr)*. Given the images of the drive, I can't see its cross section being > 1 m^2 (and the Halo flux is by no means focused), and this is thus ~6 orders of magnitude too small (and, note, also much less than a solar sail).

So, I don't see how a coupling to DM microparticles can explain the drive thrust.

* Note that that is actually independent of the mass of the DM particles, but I like to show how to work through things. Also note that if you _reflected_ the DM particles, that estimate would increase by a factor of 2, which is not nearly enough to change things.

After making several runs in an effort to assure myself that the meep model was correct with lattice size and resolution set properly, I have a result of thrust force of the EM thruster inside the stainless steel vacuum chamber, in vacuum. This is a preliminary number but interesting enough that I will share it.

Force = 0.33845 muN/Watt. That is about 1/3 of the experimental value obtained.

The fields within the vacuum chamber are pictured, attached. Again, fields are shown at the end of the 32nd half period of the magnetic source drive frequency, 1.937115E+009 Hz. The meep model for this data still used the Teflon rubber seal, though compressed by 20%.

My next task will be to remove the Teflon rubber gasket and model metal to metal contact with a small gap, and make runs as close to 0.002 inches gap size as my computer will allow. It is my understanding from Paul March's recent post that the EM thruster cavity actually tested was constructed this way. I will then remove the vacuum chamber from the model and make runs simulating the EM thruster in free space. I will be interested to see that result.

While this single run detected only 1/3 of the experimental measured value, I will brazenly write that I think we can forget about axions and dark matter. We can forget about exotic theory and consider that the thrust force likely results from a little understood characteristic of evanescent waves and the forces they generate. Please pardon me if that steps on anyone's toes, but unless there is a serious problem with meep or my model of the thruster and vacuum chamber, well, these forces obtained from integrating the differential Maxwell equations and the MST are to large to overlook.

I don't mean to say that we do not need to know what frequencies and mode shapes to drive the cavity with, we certainly do; meep can only evaluate a model. The drive frequency and cavity needs to be designed before it can be modelled in meep.

In the meantime, lets ask why 60 watts of relatively harmonic free sine-wave RF power at the 1,937.118 MHz AKA the TM212 resonant frequency in this copper frustum cavity, can only generate a paltry ~60uN, whereas the Chinese claimed to have produce 160,000uN using just ~150 watts of 2,450 MHz RF signals from a magnetron? The magnetron RF signal source that is anything but a pure sine-wave generator, that instead has a modulated FM bandwidth of at least +/-30 MHz that is also concurrently amplitude modulated (AM) with thermal electron noise.

Taking a critical look at this question, and knowing that the spectral shape of a magnetron looks like (see below) compared to a CW spike. It seems evident that a CW spike isn't the best waveform to use if you want to maximize thrust. Dollars to donuts says the Chinese are making full use of the available bandwidth of their resonant cavity by using that noisy magnetron. Magnetrons have lots of phase noise too. You can't easily use them on phased array radars because of that for example.

Now to put this idea to test, Q: What is the bandwidth of the resonant cavity and what is the 90 percent power bandwidth of the signal you are driving it with? What kind of sig gen are you using? Can it do FM? Can you do any advanced waveforms like a PSK waveform? Do you have a way to produce wideband noise or a spread spectrum carrier for your testing? Can you do any waveforms like at the bottom?

Also during researching other possible theories which could explain Emdrive we found ample literature stating that molecules acquire a kinetic momentum during the switching of the magnetic field as a result of its interaction with the vacuum field. If correct, that may well be a very significant lead. So that raises the question, how does one increase the switching rate? What about phase shifting? http://en.wikipedia.org/wiki/Phase-shift_keying

When using our current 14mm loop antenna optimized for the TM212 resonance at 1,937.118 MHz in our copper frustum, there were four RF resonances spaced +/- 30 MHz around the 2.45 GHz center frequency. And I assume that would also be the case using a higher power slot antenna in a similar location as the Chinese and Shawyer have done with their frustum resonant cavities. So yes, a wide bandwidth RF source seems to be called for and one that can be both AM and FM modulated at the same time. From my readings to date, that appears to be a hard nut to crack for solid state RF amplifiers at the desired kW power levels due to their limited RF power bandwidth capabilities, so we may be forced into using magnetrons and just learn how best to feed their 4-to-20 kV high voltage anode requirements while working in a hard vacuum. However the more difficult problems are finding ways of reducing their mass and size so we can "fly" them on our torque pendulum. Cooling the magnetrons in a hard vacuum is also another problem we need to deal with since air cooling is out of the question and liquid cooling is a giant pain to deal with as well. About the only other way to cool these beasts in a hard vacuum is to use phase change material like paraffin wax that could give us several minutes of run times before we had to let the accumulated heat in the paraffin radiate to the vacuum chamber walls.

BTW, the paraffin wax phase change cooling was used to good advantage on the lunar moon buggy used by NASA astronauts during their lunar explorations in the late 1960s and early 1970s during the USA Apollo Moon program.

Best, Paul M.

The genius of your setup is that it's using low power to suss out a very subtle effect. One of the reasons I dismiss the Chinese results is because pumping the resonant chamber with hundreds of watts creates a cone shaped space heater, which doesn't help suss out a subtle effect from amongst the thermal effects.

There are numerous ways you can introduce a wideband rf signal into your test article without resorting to big blubbering magnetrons. I suggested the modem for example, because I know that Nasa owns them (saw the Nasa FBO request to buy them online) and the rest of the govt owns hundreds of them; their modulator will create precise wideband waveforms at will, which takes care of the wideband problem and the phase shifting idea. Any L band modulator can do this. Think of them as dual use for this application. Even an expensive signal generator can't do that.

There are also commercially available RF noise sources out there. http://www.pasternack.com/high-output-noise-generators-1-2-ghz-pe8505-p.aspx albeit hopefully cheaper than this one I hope. The wideband waveform is to ensure the bandwidth of the cavity is being fully exploited, even under changes due to heat expansion. Call me crazy, but here at home, I'm just going to use the wifi on an amp from the remote camera used to view the experiment. Cheap and effective? Which reminds me, I need to spend more time doing stuff rather than reading and typing stuff if I'm ever going to get anything done.

Superb! My congratulations. Clearly, until proven otherwise, we now have to regard the anomalous results as a function of E&M interactions with the walls of the vacuum chamber.

Well, partly perhaps, but lets wait until I run the same model without the vacuum chamber. I have ran enough cases already that I feel confident that there will be forces in that case to. My question is, how much force is due only to the vacuum chamber. It takes 6 or more hours to get one number, so first I make some runs to verify the model, (I've changed the cone/base attachment, removing the Teflon gasket.) Then I'll re-run the chamber model, then I'll remove the chamber by setting its dielectric constant to 1, and run the case with it removed. It will be tomorrow at the earliest before I have that key number.

As I was recently reminded, 1) Shawyer didn't use a chamber 2) Neither did the Chinese. Regardless of how I feel about their experimental methods or motivations, they didn't use a chamber. Also evanescent modes will not couple with a structure that can't resonate at the same mode. http://forum.nasaspaceflight.com/index.php?topic=36313.msg1331719#msg1331719 Also the test article walls are way thicker than 5x skin depth thickness which rules this out. We have covered the skin depth of copper at the operating frequencies in depth in thread 1.

We can forget about exotic theory and consider that the thrust force likely results from a little understood characteristic of evanescent waves and the forces they generate. Please pardon me if that steps on anyone's toes

This is hardly a workable theory of operation. There is nothing to back it up. Just conjecture. Not even one citation. Did anyone digest the reported facts that the device's thrust can be reversed simply by changing the resonant mode and/or the placement of the dielectric puck?

However, one can also reverse this thrust vector for this copper frustum by just changing which excited resonant mode is used and/or mounting the dielectric discs at the large OD end of the cavity instead of the small OD end, see attached resonant mode map.

However, one can also reverse this thrust vector for this copper frustum by just changing which excited resonant mode is used and/or mounting the dielectric discs at the large OD end of the cavity instead of the small OD end, see attached resonant mode map.

This is non trivial.

Yes, I can see the EXB bit, but what did they actually observe ? Did they only calculate a reversal? The description and the chart seem to be at odds. (I don't get a reversal w/o moving the dielectric a lot!)

This is hardly a workable theory of operation. There is nothing to back it up. Just conjecture. Not even one citation. Did anyone digest the reported facts that the device's thrust can be reversed simply by changing the resonant mode and/or the placement of the dielectric puck?

I did so provide a citation - to meep. That citation tells us what some of the software's capabilities are.I have also provided null results from running the model completely enclosed with no leaks. The lack of forces in that case shows it is not something within the cavity internally causing the thrust.I have also cited this paper, http://wwwsis.lnf.infn.it/pub/INFN-FM-00-04.pdf several times. No feedback what-so-ever.

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However, one can also reverse this thrust vector for this copper frustum by just changing which excited resonant mode is used and/or mounting the dielectric discs at the large OD end of the cavity instead of the small OD end, see attached resonant mode map.

Perhaps I failed to mention the fact that meep solutions exhibit this characteristic. Probably because I didn't want to muddy the water toward my objective of demonstrating force, thinking perhaps it was a resolution issue.

In any case, I did run a lot of cases with various cylindrical cavities looking for a particular resonance mode. Not infrequently, I found the force reversed in sign. Now that we are confident that force reversal is a real phenomena, I'll report it when it occurs again.

And by the way, isn't a changed resonant frequency or mode the natural result from moving the dielectric from one end to the other in the tapered cavity?

I fully agree with heartily encouraging the pursuit of MEEP (or other) calculations to examine whether the EM Drive measurements are the result of evanescent waves interacting with the vacuum chamber or other components (how about the Neodymium (NdFeB Grade N42) block magnets used to dampen the oscillations of NASA Eagleworks torque pendulum, for example ?).

The paper attempts to address Tolman's paradox (Tachyonic antitelephone http://en.wikipedia.org/wiki/Tachyonic_antitelephone <<According to the current understanding of physics, no such faster-than-light transfer of information is actually possible. For instance, the hypothetical tachyon particles which give the device its name do not exist even theoretically in the standard model of particle physics, due to tachyon condensation, and there is no experimental evidence that suggests that they might exist. The problem of detecting tachyons via causal contradictions was treated scientifically>>)

I can't see how the author's attempt to address Tolman's causal paradox (involving superluminal tachyons) can be used to support the EM Drive to work in outer space without any objects or extraneous-to-the-EMDrive fields around it to interact with the evanescent waves. As far superlumnal tachyons, my understanding is that they are hypothetical particles that always moves faster than light, and no compelling evidence for their existence has been found.

The only way that Tolman's antitelephone could exist, I think, is by branching into another timeline in the context of the many-worlds interpretation of reality, and even if one were to accept that, I don't see the connection with the EM Drive.

If Marshall or others think that Recami's discussion of Tolmans's causal paradox with superluminal tachyons ( http://wwwsis.lnf.infn.it/pub/INFN-FM-00-04.pdf ) can be used to justify EM Drive motion in outer space (without any surrounding objects, or extraneous-to-the-EMDrive electromagnetic fields, to interact with the evanescent waves), I would be very interested in learning about it.

Assuming for the moment, this device works not just in a vacuum chamber, but in space...

1) The frequency necessary to generate thrust varies with the internal (?) temperature.

2) The longer this device runs, the hotter it gets - 'Star Drive' reports major heating issues with low power test setups running for a few minutes (?) at a time. We are talking about a space version running nonstop for months or even years. To me, that sounds like a pretty extreme temperature increase - hundreds (?) thousands (?) of degrees, maybe.

So...would continual high temperatures damage the frustum over time? Or other parts of the device?

And might not the high temperatures...hmmm...act somehow to 'put the brakes' on the continual acceleration - increase to the point where the required frequency for thrust becomes unattainable, or at least reduced?

Also...heat is energy, and this device, run for long periods in space, looks to produce a lot of heat. Could a portion of that heat be tapped and converted into electrical power, thus reducing the over all power requirements? Talking supplement here, not perpetual motion.

Well, since you asked, I didn't like that paper much. I have a feeling it is either wrong, or one of those papers that uses its own form of concepts so that it appears to say one thing while really saying another, but in either case it hasn't appealed to me enough to figure out exactly where it is wrong/misleading.

There are of course a number of cases where phase velocities are > c, and yet no information can be transmitted > c because the group velocity isn't. There are also cases where weird things can happen because the speed of light in a medium is < c, and energy can be transmitted faster than the speed of light _in the medium_. I feel quite certain, however, that group velocities > c mean (at least informational) time travel. I don't see anyway around that.

So, specifically

I can't see how the author's attempt to address Tolman's causal paradox (involving superluminal tachyons) can be used to support the EM Drive to work in outer space without any objects or extraneous-to-the-EMDrive fields around it to interact with the evanescent waves.

Fully agree.

As far superlumnal tachyons, my understanding is that they are hypothetical particles that always moves faster than light, and no compelling evidence for their existence has been found.

Fully agree.

Now, in this case, the entire chamber is in the near field of these 15 cm waves. Near fields can be pretty non-intuitive (for example, not weakening as 1/R^2). I would be especially wary of what's going on in the reactive near field (within 2 cm or so of the drive), which is likely to be non-intuitive even for near-fields.

Do we know if MEEP adequately models the reactive near field? I don't see signs of it in the plots, but I do not trust my intituition, so things may be fine, but I thought I would ask.

Also, please don't forget that static fields can cause forces. "It would be nice" to see a breakdown of force by cause here.

Do we know if MEEP adequately models the reactive near field? I don't see signs of it in the plots, but I do not trust my intituition, so things may be fine, but I thought I would ask.

To my knowledge, meep integrates the differential Maxwell equations so that anything addressed by the Maxwell equations is "solved" by numerical integration. This includes evanescent waves which are a solution. It integrates the Maxwell Stress Tensor similarly, so I am laboring under the impression that yes, meep does treat the reactive near fields. Some of the earlier plots I posted from a few days ago show the signs of what I think is the near field. You might look at this image, for example:http://forum.nasaspaceflight.com/index.php?topic=36313.msg1329561#msg1329561

Assuming for the moment, this device works not just in a vacuum chamber, but in space...

1) The frequency necessary to generate thrust varies with the internal (?) temperature.

From what I understand, the resonant frequency shifts with geometry (dimensions of cavity) which shifts with temperature because of thermal dilatation. Such thermal dilatation can be hard to model because of non uniform heating (depending on standing waves mode) and non linear thermo-mechanical effects (buckling...). At high Q the resonant frequencies have very narrow bands, the slightest thermal shift in geometry of cavity will throw it off a constant frequency narrow band excitation. If it is necessary to excite at resonant frequency to generate thrust then the exciting frequency has to follow temperature (indirectly, because of geometry changing). Also the electric characteristic of dielectric (if any) would change a little (a lot ?) with temperature change and modify the target frequency.

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2) The longer this device runs, the hotter it gets - 'Star Drive' reports major heating issues with low power test setups running for a few minutes (?) at a time. We are talking about a space version running nonstop for months or even years. To me, that sounds like a pretty extreme temperature increase - hundreds (?) thousands (?) of degrees, maybe.

So...would continual high temperatures damage the frustum over time? Or other parts of the device?

And might not the high temperatures...hmmm...act somehow to 'put the brakes' on the continual acceleration - increase to the point where the required frequency for thrust becomes unattainable, or at least reduced?

This is not an indefinite thermal accumulator, the higher the temperature the higher heat flow goes from the system to the cold surrounding at Tc, as for any energy dissipating system it will reach stationary equilibrium at some temperature Te.

Te ------------------- ----- --- -- -Tc ---------

Temperature rising is a transient. Passive or active radiators efficient in vacuum are heavy and bulky but not impossible : with enough "heat flow per Kelvin" a low enough equilibrium temperature is reached (for frustum and for microwave generator) and would allow the system to be operated indefinitely at constant power (and probably constant thrust). Unfortunately most (maybe not some of Shawyer's?) emdrive experiments so far have been too short in duration to show this plateau of thermal equilibrium, but this is "just" a matter of cost and weight of radiators with good dissipation.

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Also...heat is energy, and this device, run for long periods in space, looks to produce a lot of heat. Could a portion of that heat be tapped and converted into electrical power, thus reducing the over all power requirements? Talking supplement here, not perpetual motion.

Ok, time to quit while I'm behind.

Thermocouples could recover of fraction of dissipated power... not sure if it would help or impede thermal management overall.